1. Field of the Invention
The present invention relates to a plating treatment technique for performing plating while removing bubbles present in a plating solution and, more particularly, to a plating apparatus and a plating method which are suitable for an article to be plated whose plating property is greatly affected when bubbles in a plating solution adhere to the surface of the article.
2. Description of the Related Art
Wet plating treatment has thitherto been adopted in various kinds of plated articles. In wet plating treatment, it is necessary only that the basic construction be such that an article to be plated is brought into contact with a plating solution and a plating current is given. Therefore, wet plating treatment is used in a huge variety of articles to be plated and various configurations of apparatus for wet plating have been proposed.
Wet plating apparatuses are broadly divided into the following two types. One is called “the immersion type” and plating treatment is performed by immersing an article to be plated in a plating solution. The other is “the contact type,” in which an article to be plated is not immersed in a plating solution and instead only a surface requiring plating treatment is brought into contact with a plating solution in order to ensure that only the surface in contact with the plating solution is subjected to plating treatment.
Apparatuses of these two types of “the immersion type” and “the contact type” have their advantages and disadvantages. Therefore, an optimum type of plating apparatus is selected in consideration of various conditions, such as the shape and kind of an article to be plated, the surface of an article to be plated which is subjected to plating treatment, and the type of plating solution.
For example, in the case of a plate-like article to be plated such as a semiconductor wafer and a printed circuit board, a plating apparatus of “the contact type” may sometimes be adopted in consideration of the fact that only one surface is subjected to plating treatment and that automatic plating treatment is performed by continuously replacing articles of the same size to be plated. This is because this plating apparatus of “the contact type” permits easy replacement of articles to be plated and is suitable for a case where the surface of a plate-like article to be plated is only one surface.
In this plating apparatus of “the contact type,” it is necessary only that the construction be such that the target plating surface of an article to be plated can be brought into contact with a plating solution. For this reason, there are two types of this plating apparatus. In one type, an article to be plated is placed on a top opening of a plating tank with the target plating surface kept facing downward and plating treatment is performed by supplying a plating solution to the interior of the plating tank. This type can be called “the top placement type.” In the other type, an article to be plated is arranged at the bottom of a plating tank with the target plating surface kept facing upward and plating treatment is performed by supplying a plating solution to the top of the article to be plated. The latter type can be called “the bottom arrangement type.”
In the “top placement type,” it is necessary only that an article to be plated be placed on a top opening of a plating tank. Therefore, the replacement of articles to be plated is very easy and hence suitable for the automation of plating treatment. The “top placement type” is frequently adopted in mass plating treatment of plate-like articles to be plated, such as wafers. In this “top placement type,” however, a plating solution is present below an article to be plated. Therefore, this inevitably leads to the occurrence of the phenomenon that bubbles in the plating solution, i.e., bubbles of air generated from an anode during plating treatment, bubbles of air entrapped in the plating solution, etc. ascend toward the target plating surface. For this reason, measures to remove bubbles are required in order to perform uniform plating treatment.
On the other hand, in the case of “the bottom arrangement type,” a plating solution is present above an article to be plated. Therefore, bubbles in the plating solution has no effect on the article to be plated and, therefore, uniform plating treatment is possible without measures to remove bubbles. However, in this plating apparatus of “the bottom arrangement type,” the target plating surface of an article to be plated faces upward. Therefore, even after removal of the plating solution, a large amount of plating solution adheres to the surface and hence plating solution removal work becomes necessary after plating treatment. Furthermore, replacement of articles to be plated cannot be easily carried out in comparison with “top placement type.”
Thus, the conventional wet plating apparatuses of “the contact type” had problems in the removal of bubbles from a plating solution, the removal of an adhering plating solution, the replacement of articles to be plated, etc. and could not be said to be wholly satisfactory as plating apparatuses that can simultaneously meet the requirements for uniform plating treatment and easy plating treatment.